The present invention relates to a data access method in a composite computer system arranged by a mainframe, a UNIX server, a PC server, and a storage system connected to these apparatuses.
As the prior art related with the present invention, the below-mentioned techniques are disclosed:
In mainframes, the variable length format has been employed as the data recording format.
On the other hand, in open systems such as a UNIX server and a PC server other than mainframes, the fixed length format has been employed as the data recording format.
Very recently, high density and high performance of fixed length format disk apparatuses are rapidly realized.
On the other hand, "A Case for Redundant Arrays of Inexpensive Disks (RAID)" written by D. Patterson, et. al, is known from ACM SIGMOD conference proceedings, Chicago, Ill., Jun. 1 to 3, 1998, pages 109 to 116.
This Patterson's thesis describes the technique for the data location on the disk array.
A disk array is a mechanism capable of realizing high performance and high reliability of a disk system. To achieve high performance in a disk array, a plurality of physically-realized disk apparatuses have the appearance of a single disk apparatus with respect to a processing apparatus. On the other hand, in order to realize high reliability of such a disk array, when a failure happens to occur in one disk apparatus for storing data, redundant data used to recover data is stored into another disk apparatus.
Considering the above-explained concept, generally speaking, disk arrays are popularized in computer systems. Usually, disk arrays are constituted by plural disk apparatuses and a disk array controller for controlling the respective disk apparatuses.
Since the fixed length format is utilized in a UNIX server and a PC server, an interface provided between a server and a disk array controller employs a fixed length format type interface. Also, since each of disk apparatuses provided inside a disk array owns the fixed length format, an interface provided between a disk array controller and a disk apparatus employs a fixed length format type interface.
Generally speaking, in the case of a disk array used in a mainframe, while a fixed length format disk apparatus is gradually realized with having high density and a high performance, fixed length format disk apparatuses are normally employed in each of these disk apparatuses. Then, a disk array controller utilizes a cache memory and owns a fixed length/variable length conversion function, whereas both a mainframe host and a disk array controller are connected to each other by way of a variable length format type interface. As to the variable length format type interface, the input/output request issued from the mainframe is constituted by a plurality of input/output commands referred to as CCW (Channel Command Word), as described in the publication "Computer Architecture" written by Jhon Hennecy, and David Patterson, pages 546 to 553. A plurality of CCWs are referred to as a CCW chain. These CCW chains are formed by an operating system of a mainframe in response to a request from an application program.
Very recently, computer systems are normally arranged by mixture systems of mainframes, UNIX servers, and PC servers. In such a computer system arrangement, a strong demand is made as follows. That is, in order to easily manage the disk array, data to which the mainframe, the UNIX server, and the PC server separately access are commonly stored, so that the disk array is managed in a batch mode. To satisfy such a demand, a disk array equipped with both types of interfaces has been developed, namely the variable length format type interface used to be connected to the mainframe, and the fixed length format type interface used to be connected to the UNIX server and the PC server.
Also, there is a technique capable of accessing from an open system, data of a mainframe, which is stored in a disk array equipped with both a variable length format type interface and also a fixed length format type interface.
In this access technique, while the variable length/fixed length format conversion is carried out within the disk array, the data of the mainframe which has been stored into the fixed length format type disk apparatus is derived via another fixed length format type interface owned by the disk array to the server of the open system in the direct form of the data stored in the fixed length format type disk apparatus. While the variable length/fixed length format conversion is carried out on the server of the open system, the data of the main frame is derived.
On the other hand, since processors of mainframes are manufactured in CMOS structures, these processors are gradually made in low cost and compact. As apparent from "Multiprise 2000 server" marketed by IBM Corporation, the technique capable of containing the fixed length format disks into the chassis of the mainframe is disclosed. In this technique, the fixed length format disk is directly connected to the processor of the mainframe; the CCW chain produced by the operating system on the processor of another mainframe is interpreted; the fixed length format disk is accessed; the fixed length/variable length format conversion is carried out; and the input/output request is executed. It should be noted that this fixed length/variable length format conversion may be realized by employing a portion of the main memory as a disk cache memory. As a result, since the compact disks contained in the chassis of the mainframe can be utilized without changing the existing operating system (OS) and the existing application program, the mainframe can be made compact and inexpensive. A different technical point from the above-explained IBM Multiprise 2000 server is to interpret the CCW chain produced by the operating system on the processor of the mainframe. As a consequence, there is no need to change the existing operating system and also the existing application program.